Abstract: In practical geotechnical field, failure planes are always 3D curved sliding surface. Their mechanical characteristics are different from the typical flat failure plane. Curved surface shear test is taken to consider the effects of failure plane’s curvature to the shear strength of coarse-grained soils. The results show that the shear strength grows nonlinearly with the curvature radius’ growth of shearing surface, this phenomenon is defined as the effect of curvature to curved surface shear strength. The results also show that the effect of curvature is obvious in a certain range of vertical stress, and the effect will be weakened and eventually disappeared as the vertical stress increasing. Finally, the ideal sphere model is used for qualitatively analyzing the mechanism of curvature effect and the relationship between effect and grain size and particle crushing under high pressure. It also points out the prediction of the disappearance of curvature effect in fine-grained soil and under high pressure. 

Key words: Coarse Grained Soil, Curvature Effect, Curved Surface Shear, Shear Strength